Electro-optical digitizing scanners are commonly employed as peripheral devices linked with microcomputers and other data processing and storage devices. Scanners enable graphical and text data to be accurately converted into stored digital data for further processing and interpretation, by, for example, a microcomputer. Scanners are adapted to read data from a variety of media and formats. Opaque and transparent sheets are two common forms of scanned media.
An image on a sheet is defined by light areas ("highlights") and dark areas ("shadows"). To convert the light and dark areas into corresponding image data, the scanner typically illuminates the sheet with a light source. In one form of scanner, the sheet moves relative to a stationary camera by one or more sets of feed rollers. The sheet is provided to the rollers manually by placement on a feed tray. In higher-volume applications, the sheet can be stripped from a stack of sheets by a singulator assembly. As the sheet moves relative to the camera, the camera "scans" the width of the illuminated image, converting the scanned portion of the image into a data signal. This scanned image is said to be "digitized" in that the image is converted into a data file stored in a digital format with information representative of discrete segments or "pixels." The data in the file includes instructions on how to assemble the individual pixels into a cohesive two-dimensional image that mirrors the original scanned image. The data file includes information on the intensity value for each pixel and its color, if applicable, or grayscale shade.
Digitizing scanners that feed sheets through a stationary scanner generally create a non-digitizable zone near the lead edge, the trail edge, or both. This results because a single pair of feed rollers are used to grip the sheet adjacent to either the upstream or downstream side of the camera's field of view or "image line." Since the camera relies upon a fairly constant feed rate to properly scan the image, the feed rollers must maintain contact with the sheet at all times during the scanning process. To maintain contact, the rollers must, first, grip the sheet at an edge. The area adjacent to this edge is, thus, largely unscannable because of the interfering diameter of the roller.
In addition, most scanner feed mechanisms are also unidirectional, lacking the ability to precisely reverse and rescan a sheet. Accordingly, a sheet must be removed and rescanned again if another scanning operation is desired, such as scanning a portion of the sheet at a different resolution, or scanning the detail along a grip edge.
The scanning of translucent sheets is desirable in the medical field, and presents particular challenges. In particular, there is a need to digitally store and reproduce diagnostic radiological films, commonly termed "X-rays." Most patient X-ray films, in fact, are produced in a "series" that can consist of six or more individual, interrelated X-rays. Hundreds, or even thousands, of X-ray films are produced daily by a large hospital. By electronically storing and indexing radiological images, they can be made available indefinitely without taking up valuable storage space. In addition, various specialized graphical processes and image enhancement techniques can be used in connection with stored X-ray images. Furthermore, scanned radiological data can be easily transmitted to practitioners at remote locations via electronic mail or facsimile. In all, the ability to accurately and reliably scan developed X-ray film images provides an important diagnostic tool for medical practitioners.
High-volume scanning is desirable in fields like radiology. Hand-feeding of individual films into the scanner is inefficient and wastes scarce medical resources. A feeder that automatically singulates and feeds films from a stack into the scanner is preferable. However, films are traditionally difficult to singulate. Substantial static charges are built up on films, causing them to cling to each other. Conventional singulating techniques, in which sheets are slid off the top of the stack and into the feed rollers, are often ineffective on film. Most singulators fail to reliably separate stacked film sheets from each other causing a multiplicity of adhered sheets to pass into the scanner at once.
It is, therefore, an object of this invention to provide a sheet feed mechanism for a digitizing scanner that enables accurate scanning of the entire sheet without loss of image detail along a grip edge. The mechanism should enable precise reversing of a sheet and rescanning when desired. The mechanism should reliably singulate and transfer transparent and translucent film sheets from a feed stack.